The horticultural techniques used by permaculturists rely heavily on plant combinations. A guild is a harmonious assembly of plants (but it could be plants and animals) the essential characteristic being a diverse mixture (polyculture) whose elements all have a purpose. The plants are chosen to be beneficial to each other, and so it is similar to companion planting.
As with the forest garden, the design of guilds makes use of the advantages that the natural world provides such as below ground the nitrogen fixation and mycorrhizal fungi, and the dynamic accumulators such as comfrey. Above ground are flowers and berries that attract insects and birds - our natural allies in pest control. The physical structure of the guild may also allow it to provide shelter from winds and frost. It may also throw shade that could serve a purpose.
Guilds can be constructed by use of annual plants, but self-seeding tends to allow creep. Thus it is best to have a permanent plant community using perennial plants. When planting guilds, experiments and experience (observation) will tell us if it works. Plant choices can be made on their range of function (see above) but they should also be made on the particular characteristic of growth of the plant i.e. does it crowd out its neighbours by spreading aggressively? Does it expand by forming clumps, or does it spread by underground shoots or by producing a carpet? Is it stable and long lasting?
We can think of a community of plants as being a matrix having successive layers of vegetation above ground and a similar complex pattern of roots below ground (i.e. some plants have spreading roots, some have deep tap roots and others have a mat of roots in a clump). Creating plant matrices requires the ability to match plants with the habitat (i.e. soil, climate, shade etc.) and to create plant alliances that make use of the ability of plants to form mutually dependant groups. These groups occupy the ground and the space above it so successfully that intruders cannot find a way in. The closeness of planting and the eventual growing together of the different plants means that there is rarely any bare soil and so weeds are kept out. This reduces much of the work, as there is no hoeing, little ground preparation, and little need for external inputs. Because the plants form a cover, they will reduce water loss from the soil and thus the need for watering. The plants and the communities they form become the controlling factor feeding back what if any work should be done.
Establishment of a guild takes time and the character and composition of any planting changes as it develops and matures. Annuals and short-lived perennials can sometimes be used as fillers in the early stages, dying out within a few years. Woodland could be thought of as being the most completely developed guild. A micro-forest can be made mixing shrubs with perennials in mixed guilds. The shrubs can emerge like islands from the perennials, which themselves give interest before the shrub has burst into life. In fact, while we may think of a matrix as being three-dimensional, there is another dimension to consider. Different plants contribute to the matrix at different times of the year.
Two types of guilds are planted at Springfield, a community garden near Bradford. They attempt to show the integration of different plant types: Why should herbs be grown just in an herb garden, or top fruit and soft fruit all on its own? Is there a way of making pest control part of the permanent infrastructure of a vegetable garden or even amongst fruit?
LINEAR GUILDS: Raised rectangular beds (1.2m wide by 9m long), separated by paths (0.6m wide) are used for vegetable growing at Springfield. A narrower bed (0.6m wide, same length) compliments pairs of vegetable beds. These narrow beds are planted up with perennials, thus forming a linear guild which is spaced throughout the whole growing area (there are two perennial beds for every six vegetable beds). The planting of the narrow, perennial beds is carried out with a number of aims in mind. First, they should attract pest predator insects, so that the beds become bug banks. Next, it makes sense to grow green mulch material right next to the vegetable beds where it is to be used (i.e. perennial nitrogen-fixers such as clover and lucerne, and the comfries). Lastly, these narrow beds are a chance to grow herbs (both culinary and medicinal) and the few perennial vegetables available to us, giving us additional produce. In all cases, whatever the purpose of the plant, it is likely that most of them contribute to pest control through the predator attraction of their flowers.
ISLAND GUILDS: The second type of guild incorporates woody plants and either stands alone - as an island - or is part of a larger area of woody planting such as an orchard or forest garden. The characteristic of these guilds is a triangular planting, with one point of the triangle being a top-fruiting tree (apple, pear, plum, cherry, crab apple) and the other two points being fruit bushes (blackcurrant, gooseberry, worcesterberry etc.). The space around and within the triangle is then planted with many of the same perennials that are used in the linear guild. There may also be other woody plantings incorporated (such as flowering currant and willow) but these will be placed to the northern side of the guild so that they do not block out sunlight. Their purpose would be as early flowering shrubs that attract insects. They are likely to be managed by coppicing or pollarding.
The woody guilds are oases of mixed plantings that have similarities to a forest edge. The top fruit give height and they form the canopy. The fruit bushes, coppiced willow and flowering currant are a middle storey, and the understorey or groundcover is made up from both culinary and medicinal herbs, perennial flowers for pest predator attraction, some perennial food - and fertility for free from nitrogen fixers, micorrhizal associations and dynamic accumulators!
Mark Fisher - Permaculture Design course handout notes